Angular velocity sensor and method of adjusting characteristics of the sensor

ABSTRACT

In an angular velocity sensor including two oscillators, the oscillators are balanced in weight precisely, thus providing improved output characteristics. In the sensor, at least one of the two oscillators has a notch having a surface roughness of not higher than 2 μm on an edge thereof.

This Application is a U.S. National Phase Application of PCTInternational Application PCT/JP00/02562.

TECHNICAL FIELD

The present invention relates to an angular velocity sensor and a methodof adjusting characteristic of the sensor for use in attitude control ornavigation systems for moving objects, such as air crafts or vehicles.

BACKGROUND ART

A conventional angular velocity sensor is disclosed in Japanese PatentLaid-Open Publication No.11-351874.

FIG. 13 is a perspective view of the conventional angular velocitysensor. First detecting electrodes 2 are provided on side surfaces of afirst oscillator 1 made of e.g. quartz, and first driving electrodes 3are provided on a front surface. Similarly, second detecting electrodes(not shown) are provided on side surfaces of a second oscillator 4, andsecond driving electrodes 5 connected to the first driving electrodes 3on the first oscillator 1 are provided on the front surface. A joint 6unitarily connects the first oscillator 1 to the second oscillator 4 attheir respective ends. Driving wires 7 are electrically connected atrespective one ends to the first driving electrodes 3 and the seconddriving electrodes 5, and are connected at respective other ends to twodriving terminals 8. Detecting wires 9 are electrically connected atrespective one ends to the first detecting electrodes 2 and the seconddetecting electrodes (not shown), and are connected at respective otherends to two detecting terminals 10.

An operation of the conventional angular velocity sensor will beexplained.

When the first driving electrodes 3 and the second driving electrodes 5are fed via the driving wires 7 with an alternating-current voltage fromthe driving terminals 8, the first oscillator 1 and the secondoscillator 4 start oscillating along the Y axis. Then, as the angularvelocity sensor is urged at an angular velocity about the Z axis, aCoriolis force is developed on the first oscillator 1 and the secondoscillator 4 and deforms the first oscillator 1 and the secondoscillator 4 along the X axis. The deformation generates a charge to beoutput through the first detecting electrode 2 and the second detectingelectrode (not shown). The charge is then transferred via the detectingwires 9 and the detecting terminals 10 to a computer (not shown) whichdetermines an angular velocity.

When the first oscillator 1 and the second oscillator 4 are not balancedin weight, they may deform along the X axis due to the unbalance weighteven if the angular velocity sensor is not applied an angular velocityto. This causes a charge to be generated on the first detectingelectrode 2 and the second detecting electrode (not shown).

For balancing the weight between the first oscillator 1 and the secondoscillator 4 in the conventional angular velocity sensor, a rewter 11grinds edges of the second oscillator 4 and the joint 6 to make adesired size of ground portion 12, as shown in FIG. 14.

Since the rewter 11 spins to grind the edges of the second oscillator 4and the joint 6 in the conventional angular velocity sensor to make theground portion 12, a small eccentric movement of the rewter may causethe ground portion 12 to be finished with a surface roughened as courseas about 5 μm. The angular velocity sensor accordingly produce a voltageof substantially ±10 mV when no angular velocity is applied, as shown inTable 1, hence declining output characteristics of the sensor.

TABLE 1 Surface Roughness Output Voltage with Rmax (μm) No AngularVelocity (mV) Sample 1 4.8 +6.2 Sample 2 4.6 +8.2 Sample 3 4.9 +9.4Sample 4 4.7 −7.1 Sample 5 4.7 −5.4

SUMMARY OF THE INVENTION

An angular velocity sensor includes a first oscillator including atleast one of a driving electrode and a detecting electrode, a secondoscillator including at least one of a driving electrode and a detectingelectrode, and a joint coupling the first and second oscillators. Atleast one of the first and second oscillators has a notch having asurface roughness of not higher than 2 μm in an edge thereof In thesensor having the oscillators, this arrangement allows the oscillatorsto balance in weight accurately, thus being improved in its outputcharacteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an angular velocity sensoraccording to an exemplary embodiment of the present invention.

FIG. 2 is a side cross sectional view of the angular velocity sensoraccording to the embodiment.

FIG. 3 is a perspective view of a primary part, a tuning fork of theangular velocity sensor according to the embodiment.

FIG. 4 is a perspective view of the tuning fork of the angular velocitysensor according to the embodiment.

FIG. 5 is a block diagram of a circuit board of the angular velocitysensor according to the embodiment.

FIG. 6 is a schematic diagram showing an operation of the angularvelocity sensor according to the embodiment.

FIG. 7 is a schematic diagram showing an operation of the angularvelocity sensor according to the embodiment.

FIG. 8 is a waveform diagram showing an operation of the angularvelocity sensor according to the embodiment.

FIG. 9 is a side view showing a method of adjusting a characteristic ofthe angular velocity sensor according to the embodiment.

FIG. 10 is a perspective view showing a step of grinding the tuning forkof the angular velocity sensor according to the embodiment.

FIG. 11 a waveform diagram showing the step of adjusting thecharacteristic of the angular velocity sensor according to theembodiment.

FIG. 12 illustrates output voltages of a band pass filter in a monitorcircuit and of a phase shifter in a detector of the angular velocitysensor according to the embodiment.

FIG. 13 is a perspective view of a conventional angular velocity sensor.

FIG. 14 is a perspective view showing a rewter grinding an oscillator inthe conventional angular velocity sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is an exploded perspective view of an angular velocity sensoraccording to an exemplary embodiment of the present invention, and FIG.2 is a side cross sectional view of the sensor. FIG. 3 is a perspectiveview of a primary part, i.e., a tuning fork of the angular velocitysensor of the embodiment, and FIG. 4 is a perspective view of the tuningfork seen from back. FIG. 5 is a block diagram of a circuit board of thesensor.

A first oscillator 21 includes sheets of mono-crystalline quartz whichhave different crystalline axes, and has a first driving electrode 22 onits front surface, as shown in FIG. 3, and has a second drivingelectrode 23 on its back surface, as shown in FIG. 4. The firstoscillator 21 includes a first detecting electrode 24 and a seconddetecting electrode 25 both made of gold on its outer and inner sidesurfaces, respectively. A second oscillator 27 includes sheets ofmono-crystalline quartz which have different crystalline axes, and has amonitor driving electrode 27 made of gold on its front surface, and hasa third driving electrode 28 on its back surface. The second oscillator26 includes a third detecting electrode 29 and a fourth detectingelectrode 30 on its outer and inner side surfaces, respectively. A joint31 made of quartz connects one end of the first oscillator 21 to one endof the second oscillator 26. The first oscillator 21, the secondoscillator 26, and the joint 31 are unitarily integrated to a tuningfork 31 a. The first oscillator 21 of the tuning fork 31 a has a notch31 b having a surface roughness of not higher than 2 μm on one edge ofthe front surface thereof. Upon the size of the notch 31 b being varied,the first oscillator 21 and the second oscillator 26 are balanced inweight. The joint 31 is fixed to a first base 32 made of metal havingsix terminal insertion holes 33 provided therein. The terminal insertionholes 33 accept six terminals 34 electrically connected to the firstdriving electrode 22, the second driving electrode 23, the third drivingelectrode 28, the monitor electrode 27, the first detecting electrode24, the second detecting electrode 25, and the third detecting electrode29, and the fourth detecting electrode 30. As shown in FIG. 10, setbacks32 a are provided in the base 32 as facing the notches 31 b of the firstoscillator 21 and the second oscillator 26. A metal cover 35 is mountedto the outer edge of the first base 32 and accommodates the turning fork31 a including the first oscillator 21, the second oscillator 26, andthe joint 31 with the first base 32. A metal support 36 has a supportportion 37 on one side thereof for supporting the first base 32. Morespecifically, with the support portion 37 swage-locked to the first base32, the support 36 is coupled to the first base 32. The support 36 hasthree support projections 38 provided on both lengthwise ends thereof. Acircuit board 39 is joined by soldering to the support projections 38 ofthe support 36 to extend in parallel with the support 36. Electroniccomponents 40 are mounted on the circuit board 39 for controllingvoltages input to the first driving electrode 22, the second drivingelectrode 23, the third driving electrode 28, and the monitor electrode27, and for processing signals output from the first detecting electrode24, the second detecting electrode 25, the third detecting electrode 29,and the fourth detecting electrode 30.

The electronic components 40 composes a circuit shown in FIG. 5. Amonitor circuit 44 includes a current amplifier 45 for receiving acharge from the monitor electrode 27 of the tuning form 31 a, a bandpass filter (BPF) 46 for receiving a signal output from the currentamplifier 45, a rectifier 47 for receiving a signal output from the BPF46, and a smoothing circuit 48 for receiving a signal output from therectifier 47. A signal output from the smoothing circuit 48 is input toan AGC circuit 49 for amplifying and attenuating the amplitude at theBPF 46. A signal output from the AGC circuit 49 is sent to a drivecontroller 50 which then feeds the first driving electrode 22, thesecond driving electrode 23, and the fourth driving electrode 30 of thetuning fork 31 a with driving signals. A first current amplifier 51converts charges produced by Coriolis forces on the second detectingelectrode 25 of the first oscillator 21 and the fourth detectingelectrode 30 of the second oscillator 26 into voltages. Similarly, asecond current amplifier 52 converts charges produced by Coriolis forceson the first detecting electrode 24 of the first oscillator 21 and thethird detecting electrode 29 of the second oscillator 26 into voltages.A signal output from the first current amplifier 51 is added by adifferential amplifier 53 with an inverse of the signal output from thesecond current amplifier 52. A signal output of the differentialamplifier 53 is sent to another BPF 54 for allowing a signal only in adesired frequency band to pass. A phase shifter 55 delays a signaloutput from the BPF 54 by substantially 90 degrees in phase. A signaloutput from the phase shifter 55 is sent to a synchronous detector 56where a negative voltage component substantially equal in phase to thatof the signal output from the BPF 46 of the monitor circuit 44 isinverted to positive. A signal output from the synchronous detector 56is then smoothed by a smoothing circuit 56 a. A direct-current amplifier56 b amplifies a signal output from the smoothing circuit 56 a. Thesupport 36 is held from both sides by a rubber 57 having a substantiallysquared-C shape, and has a portion 59 having a decreased cross section.The portion 59 relieves a compressing force of the rubber 57. The firstbase 32, the cover 35, the support 36, the circuit board 39, and therubber member 57 are accommodated in a bottomed metal case 60, henceallowing the rubber 57 to be placed under pressure between the innerside of the metal case 60 and the side surfaces of the support 36. Themetal case 60 is shut up at its opening with a second base 61 having sixthrough holes 62 provided therein. Source terminals 63, GND terminals64, and output terminals 65 are inserted into the through holes 62 andelectrically connected with a flexible wiring sheet 39 a to the circuitboard 39.

A procedure of assembling the angular velocity sensor of the embodimentwill be described.

A tuning fork 31 a including the first oscillator 21, the secondoscillator 26, and the joint 31 is assembled by bonding sheets ofmono-crystalline quartz having different crystalline axes.

Then, gold is vapor-deposited to make the first driving electrode 22,the second driving electrode 23, the first detecting electrode 24, andthe second detecting electrode 25 on the front, back, outer side, andinner side surfaces of the first oscillator 21, respectively, and tomake the monitor electrode 27, the third driving electrode 28, the thirddetecting electrode 29, and the fourth detecting electrode 30 on thefront, back, outer side, and inner side surfaces of the secondoscillator 26, respectively.

Then, the six terminals 34 are inserted into the corresponding terminalinsertion holes 33 in the first base 32. As the holes 33 are filled withglass based insulating material (not shown), the six terminals 34 aremounted to the first base 32.

Then, the joint 31 is mounted to the first base 32, and the sixterminals 34 are then electrically connected by wire bonding of goldleads (not shown) to the first driving electrode 22, the second drivingelectrode 23, the first detecting electrode 24, the second detectingelectrode 25, the monitor electrode 27, the third driving electrode 28,the third detecting electrode 29, and the fourth detecting electrode 30.

The first base 32 is covered with the cover 35 under a vacuum conditionso as to make the space surrounded by them in vacuum.

The support 36 is then joined to the first base 32 by swage locking ofthe support 37.

When the electronic components 40 are mounted on the circuit board 39,the support 36 is joined to the circuit board 39 by soldering thesupport projections 38.

The terminals 34 of the first base 32 are electrically connected bysoldering to their corresponding electrodes (not shown) on the circuitboard 39.

Then, the circuit board 39 and the support 36 are held together assandwiched between the two portions of the substantially squared-Cshaped rubber 57 having the cross-section-reduced portion 59.

Upon accepting the second fork base 61 accept the source terminal 63,the GND terminal 64, and the output terminals 65, the through holes 62are filled with glass based insulating material (not shown) to fix thesource terminal 63, the GND terminal 64, and the output terminals 65 tothe second base 61.

Then, the circuit board 39 is electrically connected with a flexiblewiring sheet 39 a to the source terminal 63, the GND terminal 64, andthe output terminals 65.

The cross-section-reduced portion 59 of the squared-C-shaped rubber 57is picked up and compressed by a bar tool (not shown) and is installedtogether with the circuit board 39 and the support 36 in the case 60.

Finally, the opening of the case 60 is shut up with the second base 61.

An operation of the angular velocity sensor of this embodiment assembledin the foregoing procedure will be explained.

The first driving electrode 22, the second driving electrode 23, and thethird driving electrode 28 of the tuning fork 31 a are fed withalternating-current voltages. More particularly, as shown in FIG. 6, apositive voltage is applied to the second driving electrode 23 of thefirst oscillator 21, while a negative voltage is applied to the firstdriving electrode 22. This causes the first detecting electrode 24 toexpand since the crystalline axis of the quartz sheets extends along adirection of charge. Meanwhile, the second detecting electrode 25contracts since its crystalline axis extends in a direction reverseagainst the charge. The first oscillator 21 is accordingly tiltedtowards the second oscillator 26. Then, as shown in FIG. 7, a negativevoltage is applied to the second driving electrode of the firstoscillator 21, while a positive voltage is applied to the first drivingelectrode 22. This causes the first detecting electrode 24 to contractsince the crystalline axis of the quartz sheets extends in a directionreverse against the charge. Meanwhile, the second detecting electrode 25is expanded because the crystalline axis extends in a direction of thecharge. The first oscillator 21 is accordingly tilted towards theoutside.

The third driving electrode 28 of the second oscillator 26 is also fedwith an alternating-current voltage. Since being mechanically joined toeach other by the joint 31, the first oscillator 21 and the secondoscillator 26 oscillate at a velocity V equal to an eigen frequency ofthe driving direction along the lengthwise direction of the joint 31.For keeping the oscillation in the driving direction of the tuning fork31 a constant, a charge induced on the monitor electrode 27 is fed tothe current amplifier 45 converting the charge into a voltage in asine-wave form. The voltage output from the monitor electrode 27 is sentto the BPF 46 of the monitor circuit 44 for filtering the voltage toextract a resonant frequency component of the tuning fork 31 a forremoving noises and for a sine-wave (a) shown in FIG. 8. The output ofthe BPF 46 is then fed to the rectifier 47 for converting its negativecomponent into a positive voltage component, and is fed to the smoothingcircuit 48 for converting into a direct-current voltage. When the directcurrent voltage output from the smoothing circuit 48 is too large, theAGC circuit 49 attenuates the output of the BPF 46. When it is toosmall, the AGC circuit 49 supplies to the driving control circuit 50, anamplified output of the BPF 46. These operations maintains theoscillation of the tuning fork 31 a constant. While the first oscillator21 and the second oscillator 26 perform a flex oscillation at thevelocity V along the driving direction, the tuning fork 31 a rotates atan angular velocity of ω about the lengthwise extending center axis, andthe rotation generates a Coriolis force of F=2 mVω on the firstoscillator 21 and the second oscillator 26.

Controlling the size of the notch 31 b having a surface roughness of nothigher than 2 μm on the edge of the first oscillator 21, the firstoscillator 21 and the second oscillator 26 are balanced in weight aslisted in Table 2.

TABLE 2 Surface Roughness Output Voltage with Rmax (μm) No AngularVelocity (mV) Sample 1 1.8 +0.3 Sample 2 1.7 +1.6 Sample 3 1.9 +2.4Sample 4 1.8 −0.9 Sample 5 1.9 −0.7

When no angular velocity is applied to the angular velocity sensor, boththe first oscillator 21 and the second oscillator 26 receive no externalforces except along the direction of oscillation. Accordingly, theoutput voltage can be measured of ±3 mV, thus ensuring the accuracy ofthe angular velocity.

The Coriolis force induces a voltage (b) in FIG. 8 on both the firstdetecting electrode 24 and the third detecting electrode 29, and inducesa voltage (c) on both the second detecting electrode 25 and the fourthdetecting electrode 30 which is 180 degrees out of phase with thevoltage (b). The voltage (b) is then amplified by the current amplifier51, while the voltage (c) is amplified by the current amplifier 52. Thesignal output from the current amplifier 51 is sent to the differentialamplifier 53 where the signal is summed with an inverse of the signaloutput from the current amplifier 52 to develop a voltage (d). The BPF54 extracts a resonant frequency component of the tuning fork 31 a fromthe voltage (d) for removing noises. The phase shifter shifts the outputof the BPF 54 by substantially 90 degrees to output a voltage (e). Basedon the frequency of the output of the BPF 46, the voltage (e) outputfrom the phase shifter 55 is phase-detected by the synchronous detector56, and then, the voltage has its negative component converted intopositive to develop a voltage (f). The positive voltage output from thesynchronous detector 56 is smoothed by the smoothing circuit 56 a andamplified by the direct-current amplifier 56 b to output a voltage (g).The output of the direct-current amplifier 56 b is then sent as anangular velocity signal to a computer (not shown) for calculating anangular velocity.

FIG. 9 is a side view showing a method of adjusting characteristics ofthe angular velocity sensor. FIG. 10 is a perspective view of the tuningfork of the angular velocity sensor being ground with a tape. FIG. 11 isa waveform diagram for adjusting the characteristics of the angularvelocity sensor. FIG. 12 illustrates signals output from the phaseshifters in the detector and the BPF of the monitor circuit in theangular velocity sensor.

Under the condition that no angular velocity is applied to the angularvelocity sensor, if not being balanced in weight, the first oscillator21 and the second oscillator 26 are displaced perpendicularly to adriving direction even with no signal output from the monitor electrode27. Accordingly, as if a Coriolis force is generated by an angularvelocity, the second detecting electrode 25 and the fourth detectingelectrode 30 output the signal (a) shown in FIG. 11, and the firstdetecting electrode 24 and the third detecting electrode 29 output thesignal (b).

In the angular velocity sensor of the embodiment, the signal output fromthe phase shifter 55 in the monitor circuit 44 is first compared in acomparator (not shown) provided in a trimming apparatus.

Then, a tape 68 with an abrasive 67 of diamond is disposed in thesetback 32 a of the base 32 until the tape contacts with the edge of thefirst oscillator 21 of the tuning fork 31 a, as shown in FIG. 10 if thesignal from the phase shifter 55 is negative at a zero point where theoutput of the BPF 46 shifts from negative to positive, as shown in FIG.12.

At the moment, since the tape 68 is disposed in the setback 32 a, thegrinding by the tape is hardly interrupted by the base 32, and the tapecontacts with the edge of the first oscillator 21. This arrangementallows the tape 68 to be directly engaged with the edge of the firstoscillator 21 at a desired angle.

Then, as shown in FIG. 9, the tape 68 is loaded with a tension roller69. Accordingly, the tape 68 remains urged by a constant force derivedfrom the weight of the tension roller 69, thus contacting with the firstoscillator 21. As shown in FIG. 10, the tape 68 contacts particularly atan angle of about 7 degrees to the lengthwise direction of the firstoscillator 21 which is hence urged towards the joint 31 by a greaterforce. This arrangement prevents the first oscillator 21 from beingdeflected at a side towards the joint 31 and from dodging from anyexternal stress. This allows the first oscillator 21 to be precisely cutalong the edge to shape the notch portion 12.

Even when being stressed by a greater level of the external force, thetape 68 has flexibility which absorbs the force exerted on the firstoscillator 21 or the second oscillator 26. This allows both the firstoscillator 21 and the second oscillator 26 to be loaded steadily anduniformly. This prevents the first oscillator 21 from being fracturedwhen being loaded.

As being urged by the tension roller 69, the tape 68 can uniformly pressagainst the edge of the first oscillator 21 which is thus free from anexcessive stress in a moment. This prevents the first oscillator 21 frombeing fractured during the adjustment of the characteristics.

A driving roller 70 rotating forward and backward forms the notch 31 bon the tuning fork 31 a. This has the first oscillator 21 and the secondoscillator 26 of the tuning fork 31 a balanced in weight.

Driving voltages through the first driving electrode 22, the seconddriving electrode 23, and the third driving electrode 28 displace thefirst oscillator 21 and the second oscillator 26 perpendicularly to thedriving direction even if no signal is output from the monitor electrode27. As a result, the signal outputs from the first detecting electrode24, the second detecting electrode 25, the third detecting electrode 29,and the fourth detecting electrode 30 can be measured as small as ±3 mV,i.e., almost zero.

Finally, the tape 68 is wound up by rotating a tape-winding reel 71 by apredetermined amount, and then, is released from a tape-feeding reel 72by a predetermined amount. This allows an unused portion of the tape 68to contact with the first oscillator 21 and the second oscillator 26.

In the description of the method of adjusting the characteristics of theangular velocity sensor of the embodiment, the output of the phaseshifter 55 is negative at the zero point where the output of the BPF 46shifts from negative to positive. In case that the signal output fromthe phase shifter 55 is positive, the second oscillator 26 is ground atits edge for allowing the first oscillator 21 and the second oscillator26 to be balanced in weight.

INDUSTRIAL APPLICABILITY

The angular velocity sensor of the present invention includes twooscillators precisely balanced in weight, and thus, the oscillators donot receive an external force except along a driving direction while anangular velocity is not applied. This allows the angular velocity sensorto measure an angular velocity accurately.

1. An angular velocity sensor comprising: a first oscillator; a secondoscillator; and a joint coupling said first and second oscillators,wherein at least one of said first and second oscillators has a notchhaving a surface roughness of not higher than 2 μm in an edge thereof.2. A method of adjusting a characteristic of an angular velocity sensor,comprising the steps of: providing an angular velocity sensor whichincludes a first oscillator, a second oscillator, a joint coupling thefirst and second oscillators, a driving electrode provided on at leastone of the first and second oscillators, and a detecting electrodeprovided on at least one of the first and second oscillators; andforming a notch in an edge of at least one of the first and secondoscillators by grinding the edge with an abrasive implanted tape runningthereon, so that the signal output from the detecting electrode issubstantially zero when an alternating-current voltage is applied to thedriving electrode while no angular velocity is applied to the angularvelocity sensor.
 3. The method according to claim 2, wherein the tape isloaded by a tension roller.
 4. The method according to claim 2, whereinsaid step of forming the notch comprises the sub-step of running thetape on the edge of the first oscillator askew about a lengthwisedirection of the first oscillator to apply an external force to thefirst oscillator at a side towards the joint.
 5. The method according toclaim 2, wherein said step of forming the notch comprises the sub-stepof running the tape on the edge of the second oscillator askew about alengthwise direction of the second oscillator to apply an external forceto the first oscillator at a side towards the joint.
 6. The methodaccording to claim 2, wherein said step of forming the notch comprisesthe sub-steps of running the tape on the first and second oscillatorsaskew about respective lengthwise directions of the first and secondoscillators to apply an external force on the first and secondoscillators at respective sides towards the joint.
 7. An angularvelocity sensor comprising: a first oscillator having a notch formed inan edge thereof; a second oscillator; a joint coupling one end of saidfirst oscillator and one end of said second oscillator; a drivingelectrode provided on one of the first and second oscillators; adetecting electrode provided on one of said first and secondoscillators; a base having said joint mounted thereto, said base havinga terminal electrically connected to said driving electrode and saiddetecting electrode, said base having a setback, which is a recess,formed in a portion facing said first oscillator and corresponding tosaid notch for allowing a tape to pass during shaping said notch; and acover for covering said base and for accommodating said first and secondoscillators and said joint.
 8. An angular velocity sensor comprising: afirst oscillator having a first notch formed in an edge thereof; asecond oscillator having a second notch formed in an edge thereof; ajoint coupling one end of said first oscillator and one end of saidsecond oscillator; a driving electrode provided on one of said first andsecond electrodes; a detecting electrode provided on one of said firstand second electrodes; a base having said joint mounted thereto, saidbase having a terminal electrically connected to said driving electrodeand said detecting electrode, said base having first and secondsetbacks, which are recesses, formed in respective portions facing saidfirst and second oscillators and corresponding to said first and secondnotches each for allowing a tape to pass during shaping said first andsecond notches; and a cover for covering said base and for accommodatingsaid first and second oscillators and said joint.